Species, collection locations, and gene fragment information.

The numbers of individuals collected for each species at each focal collection location (Sitka, Cape Blanco, Monterey, Santa Barbara; see text) are shown, along with collections made at alternative locations or for supplementary population-level analysis. We designed two novel primers to amplify and sequence cytochrome c oxidase, subunit I (COI) in limpets; their sequences were as follows (5′– 3′): Lottia COI fwd: TTTATAGTNATGCCAGTATTAATTGG; Lottia COI rev: CTAGCGAARATNGAAGCAATTCC. Unpublished primers were provided courtesy of C. Cunningham (Duke University), T. Bell and J. Wares (University of Georgia), and D. Eernisse (California State University, Fullerton) as noted; published primer sources are cited. In most cases, the COI fragment was used for analysis; in some species amplification of this fragment was problematic due to the presence of pseudogenes or other complications. In these cases, we amplified a fragment that spanned one or more gene boundaries, resulting in a single fragment. DNA sequence data are available online in Genbank.